Add first class Javascript/Typescript support to the Mill build tool #3068

Job	Run time
test-docs	6m 32s
build-linux / run	5m 19s
build-windows / run	6m 54s
lint-autofix / run	1m 5s
itest (11, ci/test-mill-dev.sh && ci/test-mill-release.sh && ./mill -i -k __.ivyDepsTree && ./mil... / run	1m 4s
itest (17, ci/test-mill-bootstrap.sh) / run	1m 3s
linux (11, '{scalajslib,scalanativelib,kotlinlib,pythonlib,javascriptlib}.__.test', false) / run	54s
linux (11, 'example.thirdparty[{mockito,acyclic,commons-io}].local.test', false) / run	53s
linux (11, 'example.{cli,fundamentals,depth,extending}.__.local.test', false) / run	1m 6s
linux (17, '{main,scalalib,testrunner,bsp,testkit}.__.test', false) / run	1m 1s
linux (17, 'example.{pythonlib,javascriptlib}.__.local.test', false) / run	57s
linux (17, 'example.android.__.local.test', true) / run	51s
linux (17, 'example.javalib.__.local.test', false) / run	55s
linux (17, 'example.kotlinlib.__.local.test', false) / run	1m 3s
linux (17, 'example.scalalib.__.local.test', false) / run	1m 4s
linux (17, 'example.thirdparty[{fansi,jimfs,netty,gatling}].local.test', false) / run	1m 5s
linux (17, 'example.thirdparty[arrow].local.test', false) / run	1m 5s
linux (17, 'integration.{failure,feature,ide}.__.local.test', false) / run	56s
linux (17, 'integration.invalidation.__.server.test', false) / run	51s
linux (17, 'integration.invalidation.__.fork.test', false) / run	1m 5s
linux (17, contrib.__.test, false) / run	1m 2s
windows	1s
	36m 46s

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